Current responsive arrangement



Ap 4, w39. W. KRMER 2,531,378

' CURRENT RESPONSIVE AREANGEMENT Filed April 4, y19:58 2 sheets-sheet 1HQE Werner Kr er`,

pr 39. w. KRMER y CURRENT RESPONSIVE ARRANGEMBNT vFiled April 4, 195s 2sheetsfsheet 2 ZERO FOR CORE IR- "AND QURVE 25- ZERO FOR CORE ANDCURVE24.

s Attorney.

- Patented Apr. 4, 1939 UNITED STATES PATENT orrlcr.

2,153,378 CURRENT RESPONSIVE ARRANGEMENT Application April 4, 193s,serial No. 199,991

In Germany Claims.

My invention relates to current responsive arrangements and concernsparticularly apparatus for measuring and detecting direct current. f

y t is an object of my invention to provide a 5 direct current measuringarrangement of high accuracy in which the measuring instrument itselfneed not be of the same current capacity as the circuit in which thecurrent is to be measured and in which the measuring instrum ment may beinsulated from the circuit in which the current is to be measured.

It is an object of my invention to provide a` direct current measuringarrangement of' the induction type in which an auxiliary alternating l5current source is employed.

It is an object of my invention to provide a direct current measuringinstrument in which genuine transformer action is obtained so that thecurrent flowing in the measuring instrument is independent of thevoltage in the circuit in which the measured current is flowing andindependent of the voltage of the auxiliary circuit. It is a furtherobject of myinvention to provide an arrangement in which purecompensation between a.c. and d.-c. windings is provided. Other andfurther objects and advantages will become apparent as the descriptionproceeds.

In carrying out my invention in its preferred form I provide a pair ofclosed magnetic cores with alternating-current and direct-currentwindings and, I connect the alternating current windings in oppositiontoa source of alternating current in series with an alternating currentresponsive instrument. The direct-currentwindings, of course, carry thedirect current to be measured. The magnetic cores are composed ofmaterial having a substantially rectangular magnetization curve and thecores and windings are so designed that the magnetic material operates40 in the substantially horizontal portion of the magnetization curve. l

The invention may be understood more readily from the following detaileddescription when considered in connection with the accompanying drawingsand those features of the invention which are believed to be novel andpatentable ywill be pointed out in the claims appended hereto.

lIn the drawings Fig. 1a is a schematic diagram.

5'5 my invention. Fig. 3 is a `connection. diagram which a simplealternating current responsive in- April 16, 1937 (ci. 1v1-95.)

. representing connections of embodiments of Figs. 1a and 1b. Fig. 4 isa connection diagram representing a modification inthe arrangement ofFig.' 3. Fig. 5 is a schematic diagram of an embodiment of my inventionincluding windings for compensating the effect of variations inposition-of the direct current winding in the cores. Fig. 6 is aconnection diagram of another modified embodiment. Fig. 7 is a graphshowing separately one ofthe curves of Fig. 2. Like reference charactersare utilized throughout the drawings to designate like parts.

In the arrangement illustrated in Fig. 1a, there is a direct currentwinding which may be in the form of a single rod or bar II carrying adirect current whichis'to be measured, and, in inductive relation to thedirect current winding II, are a pair of magnetic cores I2 and I3. Thecores I2 and I3 are preferably laminated or are stripwound from magneticstrip material and they are shown as continuous rings surrounding thedirect current winding or rod Il. Each of the cores I2 and I3 carries analternating current winding vand preferably the windings are divided sothat the core I2 carries a plurality of alternating current windings I4and` the core I3 carries a plurality of alternating current windingsI5.l .The windings Ill of the core I2 maybe connected in. parallel andlikewise, the windings I5 of the core i3 maybe connected inparallel. Asource of alternating current I6 is provided, to which the alternatingcurrent windings of the cores I2 and I3 are connected in opposition. Themultiple group of windings Ill may be connected in series with themultiple group of windings I5. In series with the multiple groups andthe alternating current source I 6 is connected an alternating currentresponsive device Il which may take the form of a dei'lecting ammeter.

In the arrangement of Fig. lb a direct current responsive device i8 isprovided which may take the form of a DArsonval galvanometer, forexample, which may be made more sensitive than the ordinary alternatingcurrent responsive instruments, and the direct current responsive device.I8 is connected in the circuit of the alternating current source I6through the medium of a full-'wave rectifier I9 consisting of fourrectier units which are arranged in the well-known bridge or GraetzconnectionA so that the rectiiierY I9 and the direct current responsivedevice I8 together form an alternating current responsive unit.4

'Ihe cores l2 and I3 are composed of a material having a, substantiallyrectangular magnetization curve and the design is such that the corematerial is operated in a substantially horizontal portion of themagnetization curve. In Fig. 2 the curve 2| illustrates a substantiallyrectangular magnetization curve in which there is an initial portion 22substantially vertical, and remaining portion 23 substantiallyhorizontal. In the curve 2| the values of ux density are plotted alongthe vertical axis and the values of magnetizing force in ampere turnsare plotted along the horizontal axis. Thus, itis seen that when theampere turns increase above a relatively small initial value the fluxdensity reaches its maximum value Bmx and continues at this valueindefinitely.

Any suitable material for obtaining such a sub.

stantially rectangular magnetization curve may be employed. However, Ihave found that satisfactory results may be obtained by utilizing amaterial prepared by the Fried. Krupp ln-G. in Essen, Germany under thename Hyperm. Such material is an alloy of iron and nickel. Iron siliconalloy sold under the name Hyperm 4,

may also be utilized satisfactorily, which is an alloy containing 3 to 4per cent silicon cold rolled and suitably heat treated. Such materialhas its maximum permeability in the direction of the rolling andpreferably, the cores are made by winding a strip fiat-wise into a ringwhen this material is employed.l v

I have also found an alloy sold under the trade name of Mu-Metal to besatisfactory, which consists of approximately 74% nickel, 20% iron, 4%copper, 11/% chromium, and with lesser amounts of manganese andsilicon.'

Although it may seem, at first, paradoxical that pure compensation ortransformer action could take place between primary direct currentwindings and secondary alternating current windings, it may, be seenthat such a result is actually achieved in my apparatus. As alreadystated, the curve 2| in Fig. 2 represents the magnetization curve of thetransformer cores, i. e., of the material of which the cores I2 and I3are corn-a posed. The portion of the curve 23, inwhich the apparatus isoperated is substantially horizontal. For the sake of explanation, letit be assumed that the dir ect current magnetizing force of the currentin the rod II, ATDc, is of such a value as to correspond to the point Pof the magnetization curve 2|. If an alternating voltage is applied tothe secondary windingsV I4 and I5, an alternating ilux must besuperimposed upon the unidirectional ilux to correspond to the appliedvoltage.

It is also assumed that in the first half-cycle the alternating currentmagnetization, AT1, in the core I2 opposes the direct currentmagnetization, but the a.c. magnetization, AT2, in the core I3 aids thedirect current magnetization ARDC. Then as shown by the curve 2| inFig.,2, the flux or magnetic induction in the core I3 cannot risefurther since it is already saturated. The core I3 can have no eect onthe limitation of magnetizing current during the first or any oddhalf-cycle since no back voltage can b e generated in the windings I5 byincrease of uX. In the core I2,lhowever, the flux needsI to be reducedto generate the requisite back voltage for controlling the flow ofalternat- `ing .current and theI control of the alternating .currentI'takes place by reason of such ilux re- .ilction During the nexthalf-cycle, in a similiar lmanner, the fiux needs to be reduced in thecore I3 in order. to induce a back voltage of the proper polarity. Theflux in the core I3 is' represented by the heavy line curve 24 in Figs.2

aisance and 7 in which fiux is plotted along the horizontal axis andtime is plotted in the vertical direction. To avoid confusion, the iluxcurve alone has been duplicated in Fig. 7, in which O2 is the zero pointof flux and time for core l3and the distance OzQ represents the ux dueto the unidirectional magnetization ATnc by the current in the d.c.windngEL Since the a.c. windings inthe cores i2 and I3 are oppositelyconnected, the d.c. premagnetizations with respect to the a.c. circuitare opposite and the iiux in the corel l2 will remain constant duringeven half-cycles and will be reduced along a sinusoidal curve during oddhalf-cycles as shown by the dotted line curve 25 in Figs.2 and 7.However, in order to show the curves 24 and 25 in juxtaposition the zeropoint of flux and time of the curve 25 for core I2 has been placed at Oiin Fig- 7., OiQbeing with respect to the curve 25, the d.c.magnetization.

In order that the flux in the core I3 can be lowered as shown by thecurve 24 it is necessary that the direct current premagnetization OzQ becompensated by an equally strongv alternating current magnetizing force,for as seen from curve 2i, the resultant magnetizing force must fallsubstantially to zero before the flux density can be reduced from thevalue Bmx. Furthermore. the compensating alternating current will have asquare wave shape, since the portion 22 of the curve 2l is substantiallyvertical and extremely minute variation in'instantaneous magnetizingcurrent in the vicinity of zero will produce the requisite variation inaltitude of the sinusoidal portion of the flux curve 24. The currentWhich must flow in the a.c. windings i5 of the core I3 to produce the uxwave 24 is shown in Fig. 2 by the curve 26, and the current which mustflow in the a.c. windings I4 of the core I2 to produce .the ilux wave 25is shown in Fig. 2 by the curve 2l. The alternating-current windings I4and I5 function alternately in restraining the alternating currentsupplied by the voltage source I6 and the current in thealternating-circuit is shown by the composite square wave 26-2'I o-fFig. 2. The maximum value, which is also the effective value,corresponds to the current flowing in the d.c. winding II, since thea.c. magnetizations AT1 and ATz must equal the d.c. magnetization ATDc,i. e.,

where IAc is the eiective value of the current in windings ld and I5,NAc is the number of turns in either winding, Inc is the value ofcurrent in the winding II and NDc is the number of turns, in this caseonly one, since the winding II is shown as a straight bar. In Fig. 2 thealternating current 26-21 has been shown to the same scale asv thecorresponding a.c. ampere turns or magnetizing forces ATz and AT1.

From the foregoing it is seen that each of the cores i 2 and I3 developshalf the flux wave, and together they give rise to a square-wavedalternating current in the instrument I'I. The magnture of the voltage Vof the source I6, however, is Without appreciable effect upon themagnitude of the current for the reason that the current is governedonly by the amount of compensation needed to overcome the eect of theprimary or direct current. Theoretically, the voltage V may uctuatebetween the values O and 2 K Bmax without any change in alternating orsecondary current, where K is a constant dependent upon the dimensionsof the transformer, such as the number of turns, and the cross-sectionalarea of the core and Bmx is the 'altitude of the horizontal portion 23of the curve 2| in Fig. 2, expressed in Gausses. In other words, thevoltage V might have any value up to that for which the peak value ofthe flux Wave 24-25 would correspond tol a flux density of Bmx. Inpractice, however, the transformer formed by the cores and windings ofFig. la must be loaded with a burden having nite impedance. If theimpedance of the instrument Il constituting the burden is Z the minimumvalue of the voltage V of the source I6 must be greater than IAcZ,sincethe power required to energize the instrument I1 can be furnishedonly by the a.-c. supply I6.

Just as the apparatus has been shown to be independent of voltagevariation it is likewise independent of variations in excitation.

If the rectangular magnetization curve 2I of Fig. 2 is taken as thebasis for an ideal alternating-current transformer, then the directcurrent transformer heretofore described has the 4side is rectified byusing the rectifier I9, of Fig.

1b, its rectangular wave form results in a wavefree or perfectly smoothdirect current' which bears a constant ratio to the direct currentflowing in the primary winding II,

.Even great distortions of the alternating voltage exercise nonoticeable effect upon the secondary current, since they have no inuenceon the size of the compensation ampere-turns or magnetizing force.Voltage variations distort only the self-forming exciting current, whichis infinitely small, occurring as a fault current in an idealtransformer.

Fluctuations in the direct current flowing in the primary winding IIreappear as fluctuations in the maximum and effective value of therectangular a.c. wave in the secondary windings I4 and I5, in spite ofthe opposing connections of the windings on the cores I2 and I3. Thisaction takes place owing to the magnetic ineffectiveness of one or theother of the transformer cores during each half-cycle and thus perfectsthe picture ofthe pure transformer.

I'hus far the apparatus has been considered as a purely direct currenttransformervand hence loading only by an ohmic burden has been assumed.If the secondary current is rectified, as illustrated in Fig. 1b by theuse of the rectier I9, the possibility of any other type of loading'iseliminated. If the transformer of Fig. 1a without rectification of thesecondary current had its secondary windings I4 and `I5 loaded with aninductive burden, it was to be expected that the transformer would actin a way which has no parallel in connection with alternating currenttransformers. might anticipate that the vertical fronts of the secondarycurrent half-waves would be somewhat flattened evenin the case of atransformer of unlimited'outputcapacity lowing to the high impedance oflinductive loads to such waves. Consequently, in the ideal Acaseparticularly with perfectly rectangular waves, there would be' a'.possibility of a transformer fault, and.4 I consider it advantageous toemploy the rectifierIS in the secondary circuit (Fig. 1b). The ideal,perfectly rectangular, magnetization curve is With an inductive circuitone best met in practice by using a highly permeable core material witha sharp saturation bend such I I in the cores I`2 and I3 -may.vary, itis desirable to use a series parallel connection instead of a simpleseries or parallel connection, in order to maintain the alternating fluxinduction the same throughout the cores I2 and I3. With nonconcentricdirect current fields an alternating effect tends to occur between theunidirectional flux and the alternating flux as one seeks to displacethe other. Thus a weak alternating flux would tend to appear in theparts of the core saturated with direct current, contrary totheprinciple of operation of the apparatus. Normal operating conditions areobtained by subdividing the alternating current windings of each coreinto several groups having equal numbers of turns. to form a unit whichis connected'in opposition to a corresponding unit off the other core.Such connections are shown in Figs. la, 1b and 3. A modification in Itheconnections is shown in Fig. 4. With these connections the alternatingux induction is constant in every part of the ring.` If differentdirect-current field vstrengths occur in different parts of the cores I2and I3, the transformer, in effect, consists of several direct currenttransformers connected in par strengths of the direct currentampere-turns and magnetization. yWith the series parallel connection ofthe secondary windings the apparatus to a high degree is unaffected byvariations in position within the core of the .direct-current primaryconductor Il.

A simple series connection ofthe secondary winding may, howeverberetained without sacrificing the advantages of series parallelconnection, ifcompensatingwindings 28 and 29 connected in parallel inseveral groups as shown in Fig. 5 are mounted on the cores I4 and I5respectively.

It will be understood that since a material with a perfect rectangularmagnetization curve having an absolutely horizontal portion is notknown, complete conformity in practice with thev foregoing theoreticalexplanations will lnot be obtained. f However, I have found that theactual performance conforms very closely with the theoreticalassumption. When Mu-metal, for example, is employed as the corematerial, a d.c. transformer may be produced at relatively small costfor material, in whichan accuracy of r0.5 to 1 per cent isobtained overa wide load range. Even with a fluctuation in the auxiliary alternating`voltage of $30 per cent, far in excess of what might ever occr, theiiuctuation in the secondary current does not exceed r0.2 per cent.

In Fig. 6, I have shown another modification in connections'for thepurpose of compensation. It is well known to change the number v'ofturns in the secondary winding of a transformer for the purpose ofcompensation. However, this is not convenient in case severalwindingsare operated-in multiple. Accordingly-I may employ an yauxiliaryalternating current transformer 3D, which maybe an auto-transformer witha winding divided into sections 3I and 32. The primary The groups ofeach core are connected winding 3I-32 is connected in series with thecurrent source I6 Iand the a.c. transformer sec-'- ondary windings Uland l5, whereas the secondary Winding 32 is connected to the instrumentI1. Obviously, the transformer Sli may be re1atively small since theprincipal section 32 thereof carries only the small diierence currentbetween the primary and secondary currents.

I have' herein shown and particularly described certain embodiments ofmy invention and certain methods of operation embraced therein for thepurpose of explaining its principle and showing its application but itwill be obvious to those skilled in the art that many modications andvariations are possible and I aim, therefore, to cover all suchmodifications and variations as fall within the scope of my inventionwhich is defined in the appended claims.

What I claim as new and desireto secure by Letters Patent of the UnitedStates is:

1. An induction measuring system for direct current comprising a corecomposed of highly saturable magnetic material of such dimensions as tobe saturated throughout the range of direct currents to be measured, adirect-current winding in inductive relation thereto, analternatingcurrent winding also in inductive relation to said core, asource of alternating current and an instrument in series with saidsource` and said alternating-current winding.

2. An induction measuring system comprising a core composed of highlysaturable magnetic material, means for subjecting said core tounidirectional magnetizing force responsive to a quantity to bemeasured, said core and said means having-such dimensions that said coreis saturated throughout `the range of operation of the apparatus, meansfor subjecting said core to alternating magnetizing force, a source ofalternating current for energizing said latter means and a currentresponsive instrument in series with said source and s'aid latter means.

3. An induction measuring system comprising a core composed of highlysaturable magnetic arcanes material, means for subjecting said core touni-1 directional magnetizing force responsive to a quantity to bemeasured, said core and said means having such dimensions that said coreis saturated throughout the range of operation of the apparatus, meansfor subjecting said core to alternating magnetizing force, a source ofalterhating current for energizing said latter means and a rectifier inseries with said source and said latter Vmeans and a direct currentinstrument energized by said rectifier.

4. A direct-current transformer comprising a direct-current primarywinding, a core of saturable magnetic material in inductive relationtherewith, said winding and core being of such dimensions that the coreis saturated throughout the range of operation of the apparatus, analternating-current winding in inductive relation with said core, asource of alternating current, a rectifier having input terminals inseries with said source and said alternating-current winding and havingoutput terminals from which direct current is obtained.

5. An induction measuring system for direct current comprising a pair ofmagnetic cores, direct-current windings in inductive relation to saidcores and carrying a direct current to be measured, a plurality ofalternating-current windings on each of said cores, thealternatingcurrent windings of each core being connected in multiple, asource of alternating current and an alternating-current responsivedevice, said current responsive device with a multiple group ofalternating-current windings in one core and a multiple group ofalternating current windings in the second core being connected inseries to said source of alternating current, said cores being composedof material having substantially rectangular magnetization curves andbeingV operated within the horizontal portions of the curves.

' WERNER *Certiicate of Correction Patent No. 2,153,378.

April 4, 1939.

WERNER KRMER It is herebycertified that errors appear in the printed'specification of the above numbered patent requiring correctionasfollows: Page 2, first column, line 59, for ARDC readATDC; and secondcolumn, lines 65-66, for vmagniture read magnitude; and that the saidLetters Patent should be read with these corrections therein that thesaine may conform to the record of the case in the Patent Office.

Signed and sealed this 6th day of June, A. D. 1939.

Henry Van Arsdalel Acting Commissioner of Patents.

